"One or two twists in the film"

none... it was boring and formulaic

Obviously this will contain a major spoiler.

One can consider the servant boy being the main "villain" of the movie as a sort of a twist.

Ok I guess the servant being a ghost is a ‘minor’ twist but I can’t think of a second.

Maybe the Garden Room being the same Garden room he and his wife had when he finally got inside. Maybe.